An internal combustion engine typically has three chambers, the crankcase, the timing case and the top cover. Each of these chambers must be openly connected to allow free flow of bypass gases and air movement during engine running. In a closed breather system blow-by gas escapes past the piston into the crankcase where it mixes with airborne oil droplets and is fed back into the engine induction system. The blow-by gas passes through a woven mesh oil separator that separates the oil from the blow-by gas before allowing the oil to return to the sump under gravity. The blow-by gas then continues through a pressure regulation valve to the induction manifold. The pressure regulation valve typically has a spring-loaded diaphragm that closes when the induction depression overcomes the spring load. Positive crankcase pressure opens the diaphragm and allows blow-by gases to escape into the air intake system. Negative crankcase pressure closes the diaphragm and prevents blow-by gases being drawn back into the engine.
In the known closed circuit breather systems there is a reliance on gravity to ensure that oil in the blow-by gases returns to the sump. Under abnormal operating conditions, such as sump overfill or excessive blow-by of oil arising from a worn engine, there is a risk that oil may not return to the sump, but may be directed to the pressure regulation valve and hence to the engine induction system by gravity, resulting in undesirable engine emissions. If the engine is mounted in a vehicle or machine that is operated at an extreme inclination or rolls over, there is a risk that substantial quantities of oil can flow under gravity and enter the engine induction system. This can cause the engine to run in an ungoverned condition and can result in damage to the engine as well as undesirable engine emissions.
The present invention seeks to provide a shut-off valve for a breather system that overcomes one or more of these problems.